@jegergryte: Linked also has no increase in attack difficulty. auto fire results in +1 difficulty. That's a small but meaningful difference.
This update was a touch disappointing, as there isn't as much too it as I hoped for.
I guess an average enemy has soak 4-5, so an autofire hit deals minimum 6-7 damage per hit. Add a couple ranks of barrage into that mix and it gets worse. A single advantage nearly doubles that damage.
lets say you are a bodyguard with 4 ranks of ranged heavy, 2 agility, 2 ranks of barrage firing at a defel assassin at medium range uses a dice pool of 2prof and 2ability and one boost (it's only fair to assume he aims) with a 3 challange die pool (this is all assuming no allies aid, which would be their best option in this case).
The average chance of getting at least one net success and one net advantage are very good in this case. 5/8 chance of a success per ability dice, 10/12 chance with profs, 2/6 with boost. total avg success 20+20+8+15+15 = 78/24 success per roll, or about 3.25 avg success per roll. avg failure is 9/12 per challange, or 2.25 avg failure per roll.
So statisitcally on autofire the bodyguard could be expected to hit with each attack.
advantage comes up as being even more likely, with the prof dice and challange dice cancelling out, so you have 8/12 threat vs 2*(5/8)+4/6 which is 23/12-8/12 leading to a 13/12 chance of netting at least one advantage.
oops. forgot the defel's defense. With that calc'd in the bodyguard has a 66.666% chance to net a success and a 9/12 chance to net a success which is a good chance to blast theat defel assassin right out of the gate.
If even one ally aids the odds swing even farther into favor of the autofire.
In this scenario, even not autofiring only increases the chance to hit by about 12%, and the odds of advantage to about 100% chance. So autofire is easily the better option, since if it hits it's likely to kill the defel out right.
Now this is a more simplistic model of the odds, as there is a measure of degree that's harder to calc on the spot here, but My view on auto fire off the bat is make the first hit cost 2 advantage, and each additional hit cost one. this gives it a tougher hurdle than linked, but with 4 advantage it makes the damage output superior to linked and similar abilities.
I almost want to say that maybe autofire should really only be allowed to walking fire, and/or cap off the number of additional hits at 1.
tl:dr - Autofire: It's a tough call, I don't envy them devs.